1. Field of the Invention
The present application relates generally to the fields of immunology and gene delivery. More particularly, the application relates to compositions, systems and methods for producing proteins of interest, such as antibodies.
2. Description of the Related Art
Despite tremendous efforts, no effective vaccine has been developed for human immunodeficiency virus (HIV) so far. Many antibodies have been identified as capable of neutralizing most circulating HIV strains. Although substantial effort has focused on the design of immunogens capable of eliciting antibodies de novo that would target similar epitopes, it remains uncertain whether a conventional vaccine will be able to elicit analogues of the existing broadly neutralizing antibodies. As an alternative to immunization, the vector-mediated gene transfer described herein can be used to engineer secretion of the existing broadly neutralizing antibodies into the circulation.
Existing methods aimed at producing genetically encoded therapeutic proteins result in only limited levels of gene expression. For example, previous efforts to engineer humoral immunity using adeno-associated virus (AAV)-based vectors resulted in modest antibody production (Lewis et al., J. Virol. 76: 8769-8775 (2002)), which was subsequently improved through the use of alternative capsids (Fang et al. Nature Biotechnol., 23: 584-590 (2005)) and self-complementary AAV (scAAV) vectors (McCarty., Mol. Ther., 16: 1648-1656 (2008)) that increase expression at the expense of carrying capacity. Recently, scAAV vectors were used to direct expression of simian immunodeficiency virus (SIV)-neutralizing immunoadhesins consisting of small, artificially fused antibody fragments (Johnson et al., Nature Med., 15(8): 901-906 (2009)). However, the efficacy of this prophylaxis was limited by an endogenous immune response directed against the immunoadhesin proteins. In addition, the lack of effectiveness of the existing AAV-based methods can be traced to the inability of AAV vectors to transmit sequences greater than approximately 4800 base pairs in length. Dong et al., Human Gene Therapy, 7:2101-2112 (1996). This limitation of AAV vectors has made it difficult to design vectors containing both a gene encoding a therapeutic protein as well as expression promoting elements to allow for high levels of production, particularly in vivo. Therefore, there is a pressing need for the development of compact vectors and systems capable of efficiently expressing genes.